The present invention relates to a level adjustment device for vehicles with a plurality of air springs, by which a vehicle body is furnished with suspension on at least one vehicle axle, which has the following characteristics:
a source of compressed air, which, for the purpose of filling the air springs, can be connected to the air springs via an air dryer; PA1 the air dryer, for the purpose of filling the air springs, is connected on one side to the air, springs through a check valve that is open to the air springs; PA1 each air spring, for the purpose of emptying them, can be connected through the air dryer and through a pneumatically controlled first distribution valve to the atmosphere, wherein the pneumatic control input of his distribution valve is then impinged through a second distribution valve with the pressure in the air springs against a restoring force acting on the pneumatic control input; PA1 the pneumatic control input of the pneumatically controlled first distribution valve, for the purpose of ending the emptying process, can be connected to the atmosphere.
A level adjustment device of the type mentioned in the introduction is known from German patent document DE 35 42 975 C2. The level adjustment device known from this publication can be characterized as advantageous in the respect that the distribution valve through which the air escapes into the atmosphere through the air dryer for the purpose of emptying the air springs is configured as a pneumatically controlled distribution valve. Consequently, high switching forces can be exerted on this distribution valve and great flow cross-sections can be engaged using the compressed air in the air springs. If by chance the distribution valve ices up as a consequence of moisture in the air at low temperatures, the switching of the distribution valve is nevertheless possible. With the level adjustment device known from DE 35 42 975 C2, it is further seen as advantageous that in their normal condition (i.e. when the air springs are neither filled up nor empty) the air springs are separated from the air dryer on one side by a check valve open to the air springs and on the other side by an electrically controlled distribution valve, so then no air can flow from the air springs to the air dryer. Consequently, it is possible to arrange between the air springs and the air dryer a pressure sensor to which each air spring can be connected to measure pressure without the possibility of air flowing out of the air springs into the air dryer. This would lead to an undesirable loss, in pressure in the air springs.
However, it must be stated with the level adjustment device known from German patent document DE 35 42 975 C2 that, in emptying an air spring, the air is routed through the electrically controlled distribution valve, which, in the normal condition, separates the air springs from the air dryer. Since with electrically controlled distribution valves only small flow cross-sections can be engaged at a justifiable expense, a rapid emptying of the air springs, and a correspondingly rapid lowering of the vehicle (e.g. with the vehicle parked) is therefore not possible.
It is therefore an object of the invention to produce a level adjustment device in which the air springs are completely separated from the air dryer in the normal condition and in which a rapid emptying of the air springs is possible.